778 Comparative Morphology of Chordates 



edentates were of enormous size. The armored glyptodons, resembling 

 armadillos, attained a length of nearly 10 feet, and ground sloths 

 ranged in size from that of a large dog to that of an elephant (Fig. 595). 

 These xenarthran edentates were confined to the Western Hemisphere 

 and were especially numerous in South America. The African aardvark 

 (Tubulidentata), however, seems to have no special affinity to any- 

 thing else. Its origin is quite problematic. 



Typical ungulates are heavy-bodied terrestrial harbivores with 

 hoofs, digital structures well adapted for swift locomotion of large 

 animals over hard, open ground. It is by no means certain whether 

 Perissodactyla and Artiodactyla diverged from one another before 

 or after claws were replaced by hoofs. Ancient ungulates were very 

 numerous and of most diverse types. One of the oldest known and most 

 primitive groups was the Condylarthra (Fig. 596), existing in the 



Fig. 595. Ground sloth (Megalocnus). (Courtesy, American Museum of Natural 

 History. New York.) 



